In networks, like Optical Burst-Switched (OBS) networks or optical networks, packets, e.g. Internet Protocol (IP) packets, Asynchrony Transfer Mode (ATM) cells or protocol data units (PDUs), are aggregated to bursts, like electrical or optical bursts, in order to be transferred through the network. The conversion of packets into bursts takes place in a node, like an edge node, of the network according to a certain aggregation strategy. The solutions so far provide two main aggregation strategies: the aggregation strategy with timeouts and the aggregation strategy with buffer limit.
First we will discuss the aggregation strategy with timeouts. A schematic example 100 is shown in FIG. 1. In this scheme, packets 102 are added or padded to a burst 104 which is being generated in a buffer 106 until a certain timer T expires. Then the burst 108 is sent.
The second aggregation strategy 200 with buffer limit will be discussed with reference to FIG. 2. In this scheme, packets 202 are added or padded to a burst 204 which is being generated in a buffer 206 until the buffer is full. Then the burst 208 is sent.
Once the packets are transformed into bursts and sent into the network, they travel in the network through a series of switches, like electrical or optical switches, depending on the network, to a certain destination. At best, these switches have limited storage capabilities, e.g. in case of optical switches fiber delay lines, and at worst, no storage capabilities at all in the normal case. Therefore, collisions among bursts occur. In a switch are two possible causes for the blocking of a burst.
First there is blocking due to switching time. A switch needs a certain time ts in order to process the header of an incoming burst and to prepare the switching elements so that the burst will be sent to the adequate output and channel, in case of optical switches to the corresponding fiber and wavelength. This switching time ts is technology dependent. The blocking due to switching time occurs when a burst comes before the switching time ts is elapsed.
Second there is blocking due to burst overlapping. In general, a switch has a limited number of m channels per connection, in case of optical switches m wavelengths per optical fiber, going to a certain destination. A burst is blocked when on a certain outgoing connection all the m channels are busy, e.g. on a fiber all the m wavelengths are busy.
On the other hand the burst generation time at the nodes is the main cause for the delay that a packet experiences. The burst generation time is the time that a packet has to wait in the buffer at the node until the burst to which it belongs is completely generated.